How to Change Measurement Units in AutoCAD

Measurement units are one of the most fundamental settings in any AutoCAD drawing. Get them wrong and every dimension, distance, and annotation in your project is off — sometimes by a factor of 25.4. Getting them right means understanding that AutoCAD handles units in several different layers, and changing one doesn't automatically change the others.

Why AutoCAD Units Work the Way They Do

AutoCAD doesn't draw in "inches" or "millimeters" in a literal sense. It draws in generic linear units, and it's up to you to define what those units represent. A line that's 100 units long could be 100 millimeters, 100 inches, or 100 feet — depending entirely on your drawing settings.

This is why simply typing a number and assuming AutoCAD "knows" your intended unit system leads to mismatches, especially when sharing drawings between teams using different regional standards (metric vs. imperial).

The Main Places Units Are Controlled in AutoCAD

There are three primary locations where unit behavior is defined:

1. The UNITS Command (Drawing Units Dialog)

The most direct method. Type UNITS into the command line and press Enter. This opens the Drawing Units dialog box, where you can set:

• Length type — Decimal, Architectural, Engineering, Fractional, or Scientific
• Length precision — How many decimal places or fractional increments display
• Angle type and precision — Decimal degrees, degrees/minutes/seconds, radians, etc.
• Insertion scale — This tells AutoCAD what unit system to assume when inserting blocks or external references

The Insertion Scale setting is particularly important. If your drawing is in millimeters and you set this to Millimeters, AutoCAD will scale incoming blocks correctly when their source unit differs from yours.

2. The INSUNITS System Variable

INSUNITS is the underlying system variable that the Insertion Scale dropdown controls. You can set it directly from the command line by typing INSUNITS and entering a number value:

This variable only controls how blocks are scaled on insertion — it doesn't rescale existing geometry.

3. Drawing Template Files (.dwt)

If you're starting fresh, the cleanest way to work in a specific unit system is to use or create a drawing template already configured for your target units. AutoCAD ships with templates for both imperial (feet and inches) and metric (millimeters, meters) workflows. Starting from the right template avoids the need to change units after the fact.

How to Change Units in an Existing Drawing 📐

If you've already created geometry and need to switch unit systems, there's an important distinction to understand:

Changing the UNITS setting does not rescale existing geometry. It only changes how AutoCAD labels and displays new inputs.

To actually convert existing geometry from one unit system to another — say, from inches to millimeters — you need to scale the geometry using the SCALE command with the appropriate conversion factor:

• Inches → Millimeters: scale factor 25.4
• Millimeters → Inches: scale factor 0.03937
• Feet → Meters: scale factor 0.3048
• Meters → Feet: scale factor 3.2808

The workflow is:

1. Select all geometry (Ctrl+A)
2. Type SCALE, press Enter
3. Pick a base point (typically the origin, 0,0)
4. Enter the conversion factor

Then update your UNITS settings to match the new scale.

Variables That Affect How Units Display

Several other system variables influence how measurements appear without changing the underlying geometry:

• LUNITS — Controls the linear unit format (1=Scientific, 2=Decimal, 3=Engineering, 4=Architectural, 5=Fractional)
• LUPREC — Sets the precision (number of decimal places) for linear units
• AUNITS / AUPREC — Same controls for angular units
• DIMSTYLE — Dimension styles have their own unit and scale settings, independent of drawing units. A mismatch between your drawing units and your active dimension style can cause dimension text to display incorrect values even when geometry is correct

🔧 AutoCAD LT vs. Full AutoCAD

The UNITS command and the core unit-change workflow are available in both AutoCAD LT and the full version of AutoCAD. The behavior is consistent across these versions, though AutoCAD-based verticals like AutoCAD Architecture or AutoCAD Civil 3D may have additional unit controls tied to project or site settings that override or supplement the standard drawing units dialog.

The Variables That Make Every Setup Different

How straightforward this process is depends heavily on your specific situation:

• Are you working solo or in a team? In collaborative environments, changing units mid-project can break shared references and block libraries.
• Does your drawing include external references (XREFs)? XREFs carry their own unit settings. Changing the host drawing's units doesn't automatically fix a mismatched XREF.
• Are you using annotative scaling? Annotation scales are tied to unit assumptions. Switching units can shift text and dimension sizes in unexpected ways.
• Which AutoCAD version are you on? The UNITS dialog has been consistent for many versions, but the exact location of certain controls has shifted slightly in newer releases.
• Are your dimension styles configured separately? As noted, dimension styles maintain independent unit overrides, so a drawing-level unit change may not immediately affect how dimensions read.

The difference between a quick two-minute fix and a multi-step correction process often comes down to how far along the drawing is, how many external dependencies it has, and whether dimension styles were set up in sync with drawing units from the start. Each of those factors points back to the specifics of your project rather than a single universal answer.